Tumor necrosis factor alpha (TNF-α) is a pro-inflammatory cytokine that is released by and interacts with cells of the immune system. TNF-α has been shown to be upregulated in a number of human diseases, including chronic diseases such as rheumatoid arthritis, Crohn's disease, ulcerative colitis and multiple sclerosis. For example, elevated levels of TNF-α are found in the synovial fluid of rheumatoid arthritis patients and play an important role in both the pathologic inflammation and the joint destruction that are hallmarks of rheumatoid arthritis.
Human TNF-α is a 17 kDa protein, and the active form exists as a homotrimer (Pennica et al., 1984, Nature 312:724-729; Davis et al., 1987, Biochemistry 26:1322-1326; Jones et al., 1989, Nature 338:225-228). TNF-α exerts its biological effects through interaction with two structurally related but functionally distinct cell surface receptors, p55 and p75, that are co-expressed on most cell types (Loetscher et al., 1990, Cell 61:351-9; Smith et al., 1990, Science 248(4958):1019-23). p55 is also known as p55R; p55TNFR; CD120a; TNFR I; TNFR 1 and TNFRSFIa. p75 is also known as p75R; p75TNFR; CD120b; TNFR II; TNFR 2 and TNFRSFIb. Both receptors are also proteolytically released as soluble molecules capable of binding TNF-α.
Inhibition of TNF-α activity as a method of treating disease, in particular, rheumatoid arthritis, has been achieved by a number of different means using inhibitors such as antibodies and soluble receptors. Examples include etanercept, marketed by Immunex Corporation as ENBREL® which is a recombinant fusion protein comprising two p75 soluble TNF-receptor domains linked to the Fc portion of a human immunoglobulin. Infliximab, marketed by Centocor Corporation as REMICADE®, is a chimeric antibody having murine anti-TNF-α variable domains and human IgG1 constant domains. Other inhibitors include engineered TNF-α molecules which form trimers with native TNF-α and prevent receptor binding (Steed et al., 2003, Science 301:1895-1898; WO 03/033720; WO 01/64889). These current methods of inhibiting TNF-α activity block binding of TNF-α to both the p55 and p75 receptors (See, for example, Mease, 2005, Expert Opin. Biol. Therapy 5(11):1491-1504). Adalimumab, marketed by Abbott Laboratories as HUMIRA®, is a recombinant, fully human anti-TNF-α antibody (Tussirot and Wendling, 2004, Expert Opin. Pharmacother. 5:581-594). Adalimumab binds specifically to TNF-α and blocks its interaction with the p55 and p75 cell surface TNF-α receptors. Adalimumab also lyses surface TNF-α expressing cells in vitro via complement-dependent cytotoxicity (“CDC”) and antibody-dependent cell-mediated cytotoxicity (“ADCC”). Adalimumab does not bind or inactivate lymphotoxin (TNF-β). Adalimumab also modulates biological responses that are induced or regulated by TNF, including changes in the levels of adhesion molecules responsible for leukocyte migration (ELAM-1, VCAM-1, and ICAM-1 with an IC50 of 1-2×10−10 M).
Despite being a human antibody, Adalimumab can elicit an immune response when administered to humans. Such an immune response can result in an immune complex-mediated clearance of the antibodies or fragments from the circulation and make repeated administration unsuitable for therapy, thereby reducing the therapeutic benefit to the patient and limiting the readministration of the antibody.
Accordingly, there is a need to provide improved anti-TNF-α antibodies or fragments that overcome one more of these problems, for example, by generating variants with higher affinity than Adalimumab that can be administered at reduced dosages or variants with reduced immunogenicity as compared to Adalimumab.
Citation or identification of any reference in Section 4 or in any other section of this application shall not be construed as an admission that such reference is available as prior art to the present disclosure.